Absorption and transport of digitoxin in the dog.

Absorption of digitoxin «us studied in 14 fasted anesthetized dogs after administration of 50 (JLC of H-digitoxin mixed with 1 mg of unlabeled digitoxin into either the duodenum or stomach. Radioactivity was measured in portal, hepatic, and central venous plasma, thoracic duct lymph, common duct bile and urine for 5 hours after digitoxin was given. Three dogs were given a single intravenous dose of 25 fie of H-digitoxin mixed with 0.5 mg of unlabeled digitoxin, and radioactivity was measured in central venous plasma and thoracic duct lymph. Digitoxin was absorbed rapidly and uniformly from the duodenum and entered the body entirely by way of the portal vein, reaching peak concentrations in portal blood in 1 to 15 minutes. Digitoxin was absorbed erratically from the stomach. No metabolites of digitoxin were observed in selected portal venous samples subjected to thin-layer chromatography. Absorption of orally administered digitoxin into the systemic bloodstream is retarded because of highly efficient hepatic extraction of the drug and subsequent transfer into bile.